There is only one interactable box in the first level, there are more in later levels but in the first level there is only one box (And you can only hold/carry one box at a time). In the very beginning, right after you press start, there is a 14 second screen (It was originally 6 seconds but I want it to last long enough to be noticed and read) stating the controls and goal of the game (I probably could have fleshed it out a bit more, but I didn't want to get people complaining about having to sit through some tutorial level or screen...turns out I should have just added that in.))
Here is a basic info of what to do: